The present invention relates to a welding method of a Si-based material. More specifically, the present invention relates to a welding method of a Si-based material which melts (fuses) and welds a Si-based material containing a single crystal or polycrystal silicon (hereinafter, referred to simply as Si) by arc welding.
In recent years, Si-based material has shown a remarkable progress in demand for a semiconductor material, and its physical and electrical characteristics as a semiconductor has attracted special interests. In the Si-based material, a Si useful as a bulk material is growing in great demand for use in silicon wafers. Recently, these wafers have been made a large diameter, and a Si ingot, which is the source of the wafer, has come to 200 kg or more in its weight. For this reason, in a manufacturing process of the Si ingot, there is a large problem how the Si ingot should be held and carried. More specifically, in an industry detesting a pollution of metal, Si or the like is used in a handling jig or the like. However, the ingot is increased in its weight, and is made a large diameter. For this reason, it is difficult to manufacture the aforesaid jig.
Therefore, an idea has been proposed such that the Si ingot itself is subjected to machining to make the Si ingot easier to carry. However, it is difficult to subject the Si ingot to machining, and after-cleaning or the like is required; for this reason, there arises a new problems such as an increase in cost and a more complicated manufacturing process.
On the other hand, in a wafer welding technique, as disclosed in Japanese Patent Application No. 3-107853, there is an SOI wafer, such as an aligned wafer. However, a welding technique is employed in order to improve an electrical characteristic, and therefore, the purpose is different from the present invention which improves a structural characteristic.
The Si-based material is very brittle. For this reason, when a great heat is applied, the Si-based material is impactively fractured. Thus, it is considered that it is difficult to carry out fusion welding with respect to the Si-based material. Recently, by using a high energy density heat source, that is, an electron beam or laser beam, it is possible to weld the Si-based material (see Japanese Patent Application No. 9-365188). However, in the aforesaid method, the welding equipment is very expensive, and, in addition, there is a limitation such that a weldment must be treated in a vacuum chamber.
In view of the above circumstances, arc welding has attracted specific interest because it requires no vacuum chamber and is relatively cheap in its equipment. However, Si, which is a semiconductor material, has an electric resistance of 1000 ohm-cm or more at a room temperature. For this reason, in welding using arc discharge as a heat source, the Si material shows a behavior similar to an insulating material. As a result, it has been considered that fusion welding using the discharge as an indispensable arc is impossible. This is because, in general, a high resistance material such as Si does not function as an electrode for arc discharge. Therefore, it is impossible to realize fusion by directly discharging the Si-based material.